1. Field of the Invention
This invention relates to a method for burnishing a magnetic surface of a magnetic disk (i.e. the so-called "flexible disk") with an abrasive tape, and an apparatus for carrying out the method.
2. Description of the Prior Art
In general, in a conventional method for burnishing the surface of a magnetic disk with an abrasive tape, a magnetic disk is supported on a support plate, which can be rotated, and an abrasive surface of an abrasive tape is pushed against a magnetic surface of the magnetic disk in order to burnish it. Surplus protrusions of a magnetic material on the magnetic surface are thereby removed, and the magnetic surface is smoothed.
In the conventional method, the entire area of the magnetic disk is supported by the rotatable support plate. Also, the abrasive tape is backed by a backing roll, which is constituted of a metal, rubber, or the like, or by a pushing rod constituted of felt, or the like. The abrasive tape is thus pushed against the surface of the magnetic disk.
However, the conventional method described above has the drawbacks in that abrasion debris scraped out during the burnishing with the abrasive tape, dust contained in the ambient air, foreign matter, which clings to the rear surface of the abrasive tape during the production of the abrasive tape, or the like, enters between the abrasive tape and the backing roll or the pushing rod and causes abrasion streaks to occur on the burnished surface of the magnetic disk. Also, there is the risk that nonuniform portions, such as abrasion streaks, occur on the burnished surface of the magnetic disk due to adverse effects from foreign matter or protrusions and recesses intervening between the rotatable support plate and the surface of the magnetic disk opposite to its burnished surface.
Accordingly, in U.S. Pat. No. 4,656,790, the applicant proposed a method for burnishing a magnetic disk comprising the steps of: (a) rotating a magnetic disk, (b) jetting compressed air, which has a pressure adjusted for flying an abrasive tape, from a first air nozzle to the abrasive tape, the abrasive tape being thereby caused to fly and brought into sliding contact with one surface of the magnetic disk, (c) jetting compressed air, which has a pressure adjusted for pushing the magnetic disk and independently of the pressure of the compressed air jetted from the first air nozzle, from a second air nozzle to a position on the other surface of the magnetic disk, which position is opposite to the region of the sliding contact of the magnetic disk with the abrasive tape, the other surface of the magnetic disk being thereby directly pushed, and (d) thereby uniformly burnishing the region of the sliding contact of the magnetic disk with the abrasive tape. With the proposed method for burnishing a magnetic disk, foreign matter, or the like, is blown off by the compressed air, and abrasion streaks are prevented from occurring on the burnished surface of the magnetic disk.
Also, as disclosed in, for example, Japanese Unexamined Patent Publication Nos. 59(1984)-110546 and 3(1991)-276421, it has been proposed to burnish and remove protrusions from a magnetic disk by utilizing a flexural rigidity of an abrasive tape. With the proposed methods, a slack is imparted to the abrasive tape, a bent portion is formed by the slack, the bent portion having a flexural rigidity is pushed against a magnetic surface of the magnetic disk, which is being rotated, and the magnetic disk is thereby burnished. The pushing force of the abrasive tape against the magnetic disk is determined by the bending radius of the abrasive tape, the level of rigidity of the abrasive tape, or the like.
However, with the aforesaid method for burnishing a magnetic disk by utilizing compressed air, the abrasive tape is pushed against the magnetic disk by the jetted air pressure. Therefore, the rigidity of the abrasive tape is low, and a sufficient contact pressure cannot be given to the magnetic disk. Accordingly, in order for a sufficient burnishing depth to be obtained, the burnishing operation must be carried out for a long time, and therefore the efficiency, with which the burnishing operation is carried out, cannot be kept high. Also, if compressed air having a higher pressure is jetted to the abrasive tape such that a higher contact pressure may be obtained, the abrasive tape will flutter, and a stable contact pressure cannot be obtained.
The aforesaid methods for burnishing a magnetic disk by utilizing a flexural rigidity of an abrasive tape has the drawbacks in that the bent portion of the abrasive tape, which is brought into sliding contact with the magnetic disk, receives a reaction load from the magnetic disk, and the bending radius of the bent portion fluctuates. Therefore, a stable contact pressure cannot be obtained, and the magnetic disk cannot be burnished uniformly.
As described above, the conventional burnishing methods described above have the drawbacks in that efficient and uniform burnishing operations cannot be carried out.